The aim of this project is to determine the mechanism for entry of the anti-cancer drug cis-diamminedichloroplatinum II (cisplatin) into cancer cells, and how this entry is affected in drug-resistant cells. Drug-sensitive and drug-resistant liver carcinoma cells were incubated for different times (0.5 hr, 1 hr, 2 hr, 4 hr) with 400 micromolar cisplatin and 100 micrograms per ml ferric chloride. Cells were pelleted, rapidly frozen in liquid ethane and cryosectioned. Energy- dispersive x-ray microanalysis showed that ion gradients and elemental distributions were disrupted due to mechanical damage in cells that had been scraped off culture dishes. It was possible to avoid this problem by using the enzyme trypsin to release the cells more gently from the substrate. In the absence of cisplatin, cells prepared in this way were found to have normal Na/K gradients across the plasma membrane. We now plan to continue our experiments on treated cells using x-ray microanalysis to co-localize cisplatin and iron. - cisplatin, x-ray microanalysis, rapid-freezing